There is a blurb on AllPar about some of the Dude trucks having the same Vin prefix.

http://www.allpar.com/trucks/dodge/dude.html

There was a guy local to me who was trying to sell a 70/71 pickup that had the same vin. He was advertising it as a Dude, even though it had been repainted and there was no evidence at all that it ever had the stripes. To me there is a big difference between, "many Dude trucks have this vin", and "my truck has this vin, therefore it is a Dude".

I'd agree, only way to tell for sure is if it still has original paint and stripes.